Packaging of anhydrous alkali metal hydroxide



PACKAGING F ANHYDROUS ALKALI METAL HYDROXIDE Frank W. Woodman, Maplewood, La., assignor, by'mesne assignments, to Columbia-Southern Chemical Corporation, Pittsbnrgh, Pa., a corporation of Delaware No Drawing. Application May 29, 1953, Serial No. 358,567

5 Claims. (01. 53-37 the drums cannot be re-used, they must be constructed at low cost.

One trouble which has been encountered in the foregoing method is that the molten anhydrous caustic becomes contaminated with iron. This iron contamination usually results from iron linked from the drum steel because the high packaging temperatures cause establishment'of stresses in the steel, or from chemical reaction between the molten anhydrous caustic and the drumsteel. Iron contamination can be almost completely eliminated by coating the interior of the drum with a thin coating of nickel, as disclosed in rn-y'prior application 154,742, filed iApril 'l, 1950, now Patent No. 2,637,441.

'According to the present invention, this thin adherent coating of nickel-or other metal is applied to the interior of a steeldruxn by spraying-exposed metal surfiaces' of the interior of the preformed drum with an aqueous solution of a salt of nickel or other metal more electronegative than iron, i. e., one which stands lower in the electrornotive series than'iron and is less readily oxidized than iron. In the use of the term electropositive gold is considered electro-negative with respect to iron in such series. Iron reacts with the metal salt, with the result that a thin coating of the metal, having a thickness in the order of one to twenty millionths of an inch, is formed on the surfiace of the drum. Surprisingly, the extremely thin coatings of metal obtained in the present invention are just as effective in preventing iron contamination of caustic as are thicker coatings of the order of 0.001 inch. When molten anhydrous caustic soda is placed in a drum which has been coated according to this invention, there is substantially no iron contamination. The method of this invention is especially advantageous since it does not require electrodeposition of the coating and provides an extremely thin though uniform and continuous coating which results in considerable saving in cost.

The novel process of coating the interior surfaces of drums and packaging anhydrous caustic therein will now be described in detail.

The drum to be coated is first cleaned or degreased with an alkaline cleaner, such as caustic soda, sodium carbonate, or trisodium phosphate, which is circulated in the drums for about one minute. Standard cleaning solutions available on the market may be used. The drum is then washed with water, and then cleaned with acid, such as hydrochloric acid, or a commercial acid cleaning solution by spraying the interior for about one minute. The

of the drum in the solution.

acid is washed out with water, and the drum is ready for coating.

In eifec'ting the coating operation, the exposed interior metal surfaces of the drum are wet with a hot solution of a salt of the metal to be deposited without immersion This may be effected by spraying the solution on to the interior surfaces of the drum. Thus, the drum may be supported in an inverted position while the salt solution is sprayed upwardly against the top and side wall of the drum. A thin film of .the solution forms on the surface of the metal, and reaction between the solution and the metallic surface takes place. The solution trickles down along the side wall of the drum, and is collected in a container located beneath the drum. Iron goes into solution, replacing an equiva lent quantity of the metal which is deposited. A portion of the solution is purified to rid it of its iron content, and then recycled. The recycled solution is admixed with fresh salt solution. The remainder is discarded.

Methods other than spraying may be used to contact the solution with the drum. Any method by which a thin 'film of solution is formed on the interior drum surfaces may be used. Thus, a drum may be maintained in an upright position while the solution is supplied at a large number of points around the top of the drum. This may be done for example by flowing the solution into a perforated header of slightly smaller diameter than that of the drum, thence through the perforations on to the drum surface. A thin film of solution forms on the interior side wall of the drum. Solution flows downwardly along the side wall and collects on the bottom, from which it is removed, either periodically or continuously. A portion of the solution may be purified to eliminate iron and then recycled in the manner indicated above. When this process is used, a thicker coating may be obtained on the bottom of the drum than on the side. For instance, a coating 6 millionths of an inch thick on the side wall and 8 to .20 millionths of an inch thick on the bottom can be obtained.

Apotential difference between the spray head or other solution feedin'g device and the drum maybe maintained if desired. The drum is the cathode and the spray head the anode. This makes it possible to obtain a thicker coating than that obtainable merely by contact of the solution with the metallic surface of the drum, and also makes faster plating possible.

If nickel is the metal to be deposited, a solution of nickelous chloride may be advantageously used. The solution is generally at a temperature of about F., or higher, and may range up to the boiling point of the solution. The pH of the solution is usually between about 1 and 4.5.

The concentration of nickelous chloride may be varied within wide limits. Solutions containing from about 0.5 moles to about 5 moles per liter may be used successfully. The reaction which occurs between the solution and the iron surface of the drum is as follows:

thereby depositing on the surface a thin coating of nickel. Spraying is continued for about one to three minutes although shorter or longer times may be used so long as an essentially continuous coating is produced. A nickel coating 1 to 20 millionths of an inch thick is formed.

Any water soluble nickel salt, such as nickel sulfate or nickel nitrate, may be used instead of nickel chloride to deposit a nickel coating. Coatings of other metals may be formed by using a soluble salt of the metal to be deposited. Thus, a cobalt chloride solution may be sprayed on to the interior of the drum to obtain cobalt coating.

3 i The drum may be coated with silver by use of silver nitrate solution. For the purpose of this invention, the interiors of steel drums may be coated with any metal below iron in the electromotive series which has a melting point above 700 F.

Iron which goes into solution during the process can be removed therefrom by conventional methods. One such method is to oxidize the iron in solution and precipitate it as ferric hydroxide. This may be effected by adding alkali to bring the pH of the solution up to a range of about 4 to 7, and bubbling air through the solution. After the ferric hydroxide precipitate is removed, the remaining solution is acidified and then admixed with fresh solution. This method is generally quite satisfactory,

, since ferric hydroxide can be precipitated at a lower pH than most hydroxides. ThepH is maintained at a value low enough to permit precipitation of ferric hydroxide and too low to cause precipitation of the, hydroxide of the other metal present.

After theinterior of the drum has been coated, it is washed with water to remove all traces of salt solution. It is 'then heated with steam dried with air, filled with molten anhydrous caustic whose temperature is between about 640 and 700 F. and then closed.

The details given in the foregoing specification are illustrative of the present invention and are not limitative except insofar as they are so expressed inthe appended claims.

What is claimed:

1. The method of packaging anhydrous caustic soda in a steel drum which comprises non-electrolytically contacting the interior surfaces of said drum with a solution of a salt of a metal less electropositive than iron whereby a very thin coating of less than 0.001 inch of the metal is formed on the said surfaces, filling said drum with anhydrous caustic soda and closing said drum.

2. The method of packaging anhydrous caustic soda in a steel drum which comprises spraying a solution of a salt of a metal less electropositive than iron onto the solution, continuing spraying until a coating of desired thickness is formed on said drum surfaces, and thereafter filling said drum with caustic soda and closing said drum.

3. The method of packaging anhydrous caustic sodain a steel drum which comprises non-electrolytically con tacting a solution of a salt of a metal less electropositive than iron with the side walls of said drum while maintaining said drum in upright position, whereby a very thin coating of less than 0.001 inch of the metal is formed on the inner surfaces of the drum, collecting the solutionon the bottom of said drum, removing said solution therefrom, and thereafter filling said drum with caustic soda and closing said drum.

4. A method of packaging anhydrous caustic soda in a steel drum which comprises nonelectrolytically contacting the interior surfaces of said drum with an aqueous solution of nickelous chloride containing between about 0.5 mole and 5 moles per liter of the nickelous chloride at a temperature of from about F. up to the boiling point of said solution, whereby a very thin nickel coating of less than 0.001 inch thickness is formed on said surfaces, removing said solution from the interior of said drum, filling the drum with molten anhydrous caustic soda and closing said drum.

5. The method of packaging an anhydrous alkali metal hydroxide in a steel drum which comprises non-electrolytically applying to the interior surfaces of the drum 2. solution of a salt of a metal less electropositive than iron whereby to form a very thin coating of the metal of less than 0.001 inch thickness on said surfaces, filling said drum with molten anhydrous alkali metal hydroxide and closing said drum.

References Cited in the file of this patent UNITED STATES PATENTS 52,465 Taylor Feb. 6, 1866 1,207,218 Roux Dec. 5, 1916 1,697,320 Mallinckrodt et a1. Jan. 1, 1929 1,814,718 Mallinckrodt et al July 14, 1931 1,829,529 Mallinckrodt et al Oct. 27, 1931 1,961,936 Mallinckrodt et a1 June 5, 1934 2,560,979 Pessel July 17, 1951 2,587,744 Mallinckrodt et a1 Mar. 4, 1952 2,637,441 Woodman May 5, 1953 2,695,249 Sweo Nov. 23, 1954 

1. THE METHOD OF PACKAGING ANHYDROUS CAUSTIC SODA IN A STEEL DRUM WHICH COMPRISES NON-ELECTROLYTICALLY CONTACTING THE INTERIOR SURFACES OF SAID DRUM WITH A SOLUTION OF A SALT OF A METAL LESS ELECTROPOSITIVE THAN IRON WHEREBY A VERY THIN COATING OF LESS THAN 0.001 INCH OF THE METAL IS FORMED ON THE SAID SURFACES, FILLING SAID DRUM WITH ANHYDROCUS CAUSTIC SODA AND CLOSING SAID DRUM. 